Stabilizing Ca-ion batteries with a 7000-cycle lifespan and superior rate capability by a superlattice-like vanadium heterostructure

Calcium-ion batteries (CIBs) by their strong competitiveness in cost and capacities have been considered as a desirable electrochemical energy technology. Nonetheless, the large ion radius and high charge density of Ca2+ lead to sluggish electrochemical reaction kinetics and structural collapse of electrode materials. Herein, we construct a superlattice-like poly 3,4-ethylenedioxythiophene−V2O5 (P–V2O5) heterostructure using an in situ self-assembly strategy and employ it as a CIB cathode. In the heterostructure, the inserted poly 3,4-ethylenedioxythiophene enlarges the interlayer of V2O5, exposing abundant active sites for efficient Ca2+ absorption and transport; meanwhile, it serves as an ‘interlayer linker’ between neighboring layers, which alleviates the volume change of V2O5 during Ca2+ insertion/extraction processes. Under the synergistic effect of these factors, the P–V2O5 electrode exhibits a longer life span and greater rate capability than pristine V2O5. Specifically, the electrode delivers a significant capacity of 157.2 mAh/g at 1 A/g and excellent cycle stability over a long period of 7000 cycles at a high current density of 20 A/g. Furthermore, it has a superior rate capability of 129.0 mAh/g even at 30 A/g. Electrochemical mechanism studies reveal that the insertion/extraction of Ca2+ in P–V2O5 is highly reversible, accompanied by the interlayer contraction/expansion.